fn f(i : i32) -> i32 {
    let (mut a, mut b) = (1, 1);
    if i <= 1 {
        return 1;
    }

    let mut start = 0;
    let mut tmp = 0;
    while start < i-1 {
        tmp = a+b;
        a = b;
        b = tmp;
        start += 1;
    };

    return tmp;
}
fn main() {

    let f1 = f(1);
    println!("f(1)={}", f1);
    println!("f(2)={}", f(2));
    println!("f(3)={}", f(3));
    println!("f(4)={}", f(4));
}
